What does "self lit" mean, and why is it a good thing?
It refers to models that already have the lights prebaked using lightmaps or pre-render all the model and bake it into a texture. Both are useful for real-time visualization of static scenes, since it can show photorrealistic results without have to render everything everytime. You can get more information about in the links below:

Lightmap: https://en.wikipedia.org/wiki/Lightmap

Baking: https://www.youtube.com/watch?v=sB09T--_ZvU